When attempting to separate particulate matter from a fluid, it is known that very small (slowly settling) particles are exponentially more difficult to separate by centrifugation than larger particles. Accordingly, most disc-type centrifuges are designed to spin at extremely high speeds in order to separate the smallest particles at a reasonable rate. High speeds mean high stress on the equipment and on the particulate matter being separated. On the other hand, it is not always necessary for a centrifuge to be capable of separating extremely small particulate matter, especially if the operator is only interested in larger material.
However, there has not been any consideration given in the past to a disc-type centrifuge dedicated to larger particle separation such that the centrifuge could operate at relatively low speeds, resulting in less stress on the equipment and permitting the utilization of less exotic construction material and techniques.
Commonly assigned Canadian patent application Ser. No. 579,008 filed Sep. 30, 1988, and its corresponding U.S. Pat. No. 4,961,724 issued Oct. 9, 1990, discloses and claims a low speed particle concentrator or centrifuge which overcomes the above-enumerated problems. That device in its preferred embodiment calls for the centrifuge to be mounted on a container whereby the recycle fluids are returned under gravity to the container by way of a circumferential array of channels. The device also calls for the upper bowl to separate completely from the lower bowl during operation thus isolating the lower bowl and associated conduit means from direct linkage to the drive means thereby requiring thrust bearing means accompanying both upper and lower bowl assemblies to receive forces generated axially during operation and permit the lower bowl to rotate solely under the influence of fluid drag. However, there are circumstances where it would be necessary to apply frictional force to the lower bowl assembly such as to limit its freedom of rotation. One such circumstance would be where the associated conduit means must sealingly engage a stationary conduit so as to receive feedstock from a deep or remote container. Another such circumstance would be where the associated conduit means must sealingly engage the centrifuge housing to permit the housing to be pressurized separately from the container to partially counteract hydrostatic forces and allow the centrifuge to be operated at higher than usual speeds.